This invention relates to a novel process for the preparation of heterocyclic diamine single-sided condensation products by condensating a pyridyl compound with a heterocyclic diamine compound. For example, condensating 2-chloro-5-chloromethyl pyridine with 2-nitroimino imidazolidine to form the corresponding compound, imidacloprid.
U.S. Pat. Nos. 4,742,060 and 6,465,492 disclose heterocyclic diamine compounds with the formula (I) 
wherein n=0 or 1; X=N or Cxe2x80x94R7, R7 is hydrogen; Y=NO2 or SO2R8, R8 is hydrogen, a C1-C4 alkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, or an aryl group; Z=pyridyl group optionally substituted by a halogen atom; R=hydrogen or methyl group; R1 to R8=hydrogen.
The above heterocyclic diamine compounds are useful as pesticides. At present, the most widely used compound is imidacloprid, a neonicotinoid insecticide. These compounds can be synthesized by reacting a pyridyl compound with a heterocyclic diamine compound in the presence of an alkali base in an organic solvent. The alkaline base can be NaH or an alkali carbonate. However, NaH is preferred over alkali carbonate for this single-sided condensation reaction because it produces a better yield. When alkali carbonate is used in the aforementioned condensation reaction, a relatively large amount of byproduct is produced. This condensation reaction can be represented as follows: 
wherein H is a halogen atom, e.g. chlorine.
However, using NaH increases cost and gives rise to safety hazards and transportation problems. Due to these drawbacks, a two-step reaction process had been proposed: react a pyridyl compound with ethylenediamine to form an intermediate that is treated with S-methyl-N-nitroisothiourea to afford a single-sided condensation product. Although this method overcomes the safety concerns and transportation problems from using NaH, the two-step reaction process is complicated, costly, and unpractical.
U.S. Pat. No. 6,307,053 discloses another process for preparing imidacloprid. A stoichiometric amount of 2-chloro-5-chloromethyl pyridine is gradually added into a mixture of a corresponding stoichiometric amount of 2-nitroiminoimidazolidine and the organic solvent in the presence of an alkali carbonate under reflux condition. The yield of 90% imidacloprid from 2-chloro-5-chloromethyl pyridine is 90xcx9c92%. i.e. active yield is 81-83%. However, the purity of imidacloprid thus obtained is less than 95%, as required by the specification. Therefore, imidacloprid needs further purification before use.
This invention provides a process for preparing heterocyclic diamine single-sided condensation products to overcome the aforesaid disadvantages. This preferred process can improve yield, minimize double-sided condensation byproduct, and produce high-quality product.
The process comprises of gradually co-feeding stoichiometric amounts of a pyridyl compound and a heterocyclic diamine compound simultaneously into an organic solvent in the presence of an alkali carbonate while heating. Due increased reactant concentrations, the molecular collision probability increases, which improves mass transfer, increases reaction rate, and minimizes byproduct formation.